Cell division and cancer

Red blood cells

Blood vessels

The tubes through which blood is carried around the body eg arteries, veins and capillaries

Chemotherapy

Treatment of disease using medicines that destroy cancer cells

Radiotherapy

Treatment of disease using X-rays or radioactive substances which kill cells

Bone marrow

Found in the centre of bones, it contains adult stem cells which divide and differentiate to produce red and white blood cells

Neurones

Cells adapted to carry information in the form of electrical impulses

Hormone

A chemical messenger produced by a particular gland or cells of the endocrine system. Hormones are transported throughout the body in the blood stream but they produce a response only in specific target cells

Tissue

A group of cells in an organism that are specialised to work together to carry out a particular function.

Liver

A large organ in the upper abdomen which manufactures, stores and breaks down substances as required by the body

Cell division, mitosis and cancer

Multi cellular organisms, like humans, are made up of billions of cells. These cells need to divide and copy themselves for a variety of reasons. For example:

cells wear out and need to be replaced

new cells allow the body to repair damaged tissue

new cells allow the body to grow

Mitosis

The most common form of cell division is called mitosis. It is used for growth and repair. During mitosis, a cell makes an exact copy of itself and splits into two new cells. Each cell contains an exact copy of the original cell's chromosomes in their 23 pairs. This is the reason why all the cells in an organism are genetically identical.

Cancer: mitosis out of control

Mitosis is closely controlled by the genes inside every cell. Sometimes this control can go wrong. If that happens in just a single cell, it can replicate itself to make new cells that are also out of control. These are cancer cells. They continue to replicate rapidly without the control systems that normal cells have. Cancer cells will form lumps, or tumours, that damage the surrounding tissues. Sometimes, cancer cells break off from the original tumour and spread in the blood to other parts of the body. When a tumour spreads to another part of the body it is said to have metastasized. They continue to replicate and make more tumours. These are called secondary tumours.

Medicines that are used to treat cancer are sometimes aimed at killing cells that are rapidly dividing by mitosis. They inhibit the synthesis or function of DNA - this type of treatment is called chemotherapy. More modern medicines target specific cancers in different ways. Many inhibit the growth signals for that type of cell.

Fighting cancer: stopping tumour cells from growing

There are many different types of cancer. They depend on which type of cell was the original one that started to replicate out of control. This means that there is not just one treatment for cancer. Treatments may include a combination of surgery, medicines and radiation therapy (radiotherapy).

As researchers have come to understand more about cancers, new and targeted therapies are constantly being developed. For example, a type of breast cancer that is influenced by the hormone oestrogen can be treated with hormone therapy that blocks the action or synthesis of oestrogen. Other medicines can block growth signals to the cancer cell and so slow the development of a tumour or block the growth of new blood vessels into tumours. This effectively 'starves' the cancer cells of the nutrients they need to grow.

Question 3

Mitosis is involved in the growth, repair and replacement of cells. Not all cells go through mitosis at the same speed.

Look at the types of cell below and decide how often they are replaced by mitosis. In each case, choose an answer using the radio buttons.

Constantly

Every few months

When damaged

Only once in a lifetime

Hair cells

(The correct answer is: 'Constantly')

(Comments: 'Hair grows every day.')

Muscle cells

(The correct answer is: 'Once in a lifetime')

(Comments: 'Can increase in size but not number.')

Cells lining the small intestine

(The correct answer is: 'Constantly')

(Comments: 'These are knocked off as food passes through the intestine and so they need constantly replacing.')

Liver cells

(The correct answer is: 'When damaged')

(Comments: 'Liver damage can be repaired so long as it is given time to heal. The liver is a vital organ and sometimes this is not possible as the damage is fatal.')

Sensory and motor nerves (neurones)

(The correct answer is: 'Once in a lifetime')

(Comments: 'Damaged nerve cells cannot be replaced.')

Skin cells

(The correct answer is: 'Constantly')

(Comments: 'These are scraped off and so they need constantly replacing.')

Red blood cells

(The correct answer is: 'Every few months')

(Comments: 'Each red blood cell lasts for around 90 days before it is replaced. New red blood cells are made 'stem cells' in the bone marrow. By the time they get into the blood, they have lost their nucleus and cannot undergo cell division.')